The T cell membrane glycoproteins, CD4 and CD8, interact with the tyrosine protein kinase, p56lck, in T cells. This interaction supports a transmembrane signalling function for CD4 and CD8 that could play an important role in T cell development and activation. It is the goal of this proposal to analyze the structure of these protein complexes and their function in the normal and diseased immune system. Specifically, we hope to reconstitute various CD8 complexes composed of CD8alpha (lyt2) CD8beta (lyt3), CD1a and class I histocompatibility antigens and test each type of complex for its ability to bind p56lck. Expression of these different forms of CD8 are developmentally regulated and could modulate signalling by p56lck. We would also like to define domains of p56lck which interact with the cytoskeleton. Such an interaction could play a role in the assembly of protein complexes containing p56lck or could play a role in the reorganization of membrane proteins that occurs during T cell activation. Lastly, we would like to determine the requirements for reconstitution of the CD8alpha/p56lck complex in vitro using peptides that correspond to the binding domains. Reconstitution in vitro would allow us to test whether a metal ion might be involved in the interaction as suggested by our earlier data. To study the function of p56lck during T cell activation, we propose to 1) determine if the kinase activity of p56lck is altered by T cell activation and what the substrates of p56lck might be, and 2) determine the effect of downregulating p56lck expression on T cell activation using anti-sense RNA strategies. Because signalling mediated by CD4 may play a role in the immune dysfunction that accompanies infection with HIV, we hope to investigate whether HIV gp120 binding to CD4 is sufficient to generate a signal transduced by p56lck. Aberrant signalling through CD4 could play a role in HIV pathogenesis.